Cacbohydrat

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CACBOHYDRAT
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CÁC ĐẠI PHÂN TỬ
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CARBOHYDRATES
Sugars and their polymers
General formula ~ (CH2O)n
C:H:O ratio 1:2:1
Possess numerous polar covalent bonds
Form H-bonds
Interact favorably
with water
Hydrophilic
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ROLES OF CARBOHYDRATES
Key roles of carbohydrates
Short-term energy storage
Longer-term energy storage
Structural roles
Cell communication
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ROLES OF CARBOHYDRATES
Short-term energy storage
Monosaccharides (“simple sugars”) are the simplest carbohydrates
e.g., Glucose, fructose,
galactose, ribose, etc.
Readily burned to release
energy
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ROLES OF CARBOHYDRATES
Short-term energy storage
Disaccharides consists of two
covalently linked monosaccharides
e.g., Sucrose, lactose, maltose, etc.
Readily hydrolyzed to form monosaccharides
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LACTOSE INTOLERANCE
Virtually all humans can digest lactose during infancy and early childhood
Milk is an important food source early in life
Infants produce the enzyme lactase
Hydrolyzes lactose into the monosaccharides glucose and galactose
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LACTOSE INTOLERANCE
Production of insufficient amounts of lactase results in lactose intolerance
Lactose intolerance is due to lactase insufficiency
Various symptoms
Nausea, cramps, bloating, gas, diarrhea, etc.
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LACTOSE INTOLERANCE
Lactose intolerance is the normal situation for adult humans
Lactase production generally begins to decline at about age 2
Lactase production generally halts by about age 4
Similar declines seen in
other mammals
Such individuals become
lactose intolerant
X
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LACTOSE INTOLERANCE
The frequency of lactose intolerance varies widely throughout the world
Over 90% of humans overall
~4% of Swedes
~100% of individuals from certain African and Asian populations
Why do these
rates differ so
widely?
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LACTOSE INTOLERANCE
Domestication of plants and animals began rather recently
Sheep, cattle, wheat, and barley were domesticated slightly over 10,000 years ago in the Near East
Profoundly altered the way people lived
Populations settled down and
cultivated their own food
Populations began to grow
Cattle, sheep, grains, and lifestyle
reached Western Europe a few
millennia later
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LACTOSE INTOLERANCE
Mutations causing lactase to be produced throughout adult life occurred in Western Europe
This mutation was beneficial in populations involved in intensive dairy farming
Natural selection increased its frequency in such populations
Lactose tolerance evolved in environments where milk is a major source of nutrition
A similar mutation also occurred in the Fulani people of Western Africa a couple thousand years ago
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LACTOSE INTOLERANCE
Dairy farming was the cultural practice that drove the evolution of lactose tolerance
Highest levels of lactase deficiency in Asian populations not involved in dairy farming
Low levels of lactase deficiency in European populations with long histories of dairy farming
Low levels of lactase deficiency in West African populations relying extensively on milk in their diets
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LACTOSE INTOLERANCE
Western Europeans colonized other areas of the world over the past five centuries
Gene conferring lactase traveled with them
Frequency of lactose tolerance increased in contacted populations
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ROLES OF CARBOHYDRATES
Longer-term energy storage
Starch and glycogen are storage polysaccharides
Plants store excess sugars as starch
Animals store excess sugars as glycogen
Monosaccharides can be released via hydrolysis
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ROLES OF CARBOHYDRATES
Structural roles
Cellulose is a major component of plant cell walls
Most abundant organic compound on earth
Polymer of glucose
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ROLES OF CARBOHYDRATES
Structural roles
The covalent linkages between monomers differ between starch and cellulose
Different three-dimensional shapes
Linkages between starch
monomers are easily hydrolyzed
Very few organisms can
hydrolyze linkages between
cellulose monomers
Lack the required enzymes
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ROLES OF CARBOHYDRATES
Structural roles
Some microbes can digest cellulose
e.g., Cellulose-digesting bacteria in a cow’s rumen
e.g., Cellulose-digesting microbes in a termite’s gut
These relationships are examples of mutualism
Both organisms benefit from the interaction
How?
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ROLES OF CARBOHYDRATES
Structural roles
Chitin is a major component of fungal cell walls and arthropod exoskeletons
Hardened with calcium carbonate in arthropods
Structure similar to cellulose
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ROLES OF CARBOHYDRATES
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ROLES OF CARBOHYDRATES
Cell communication
Glycoproteins and glycolipids on cell surface
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TÀI LIỆU THAM KHẢO
Campbell, Neil A. and Reese, Jane B. Biology, 7th edition. Pearson Education, Inc. 2005.
Campbell, Neil A., Reese, Jane B., Taylor, Martha R., and Simon, Eric J. Biology, Concepts and Connections, 5th edition. Pearson Education, Inc. 2006.
Nester, Eugene W., Anderson, Denise G., Roberts, C. Evans Jr., and Nester, Martha T. Microbiology, A Human Perspective, 5th edition. McGraw-Hill Companies, Inc. 2007.
Limson, Janice. 2002. http://www.scienceinafrica.co.za/2002/june/lactose.htm